1. Field of the Invention
The present invention relates to techniques for diagnosing a booster of a braking system for an automotive vehicle.
2. Discussion of the Related Art
JP-A-4-56669 discloses an example of a known technique for diagnosing a vacuum booster of a vehicle braking system, for any abnormality. This known diagnosing technique is based on a fact that the vacuum booster becomes inoperative to perform a normal boosting function when a negative pressure of a negative pressure source to which the vacuum booster is connected has been raised above a predetermined upper limit. According to the known diagnosing technique, a pressure switch is used to either mechanically or electrically detect that the negative pressure of the negative pressure source has exceeded the upper limit.
A study of the present inventors has revealed that when the vacuum booster is abnormal, the input and the output of the booster do not have a predetermined or known nominal relationship, and that this fact can be utilized to effect a diagnosis of the booster for any abnormality.